1. Field of the Invention
This invention relates to a well apparatus and, in particular to a pressure control device for the controlled containment and release of entrapped pressure in a plugged tubing string as the string sections are uncoupled.
2. Description of the Prior Art
In the operation of an oil or gas well in which production is obtained through tubing extending through a larger size casing, it often becomes necessary for the operator to extract the tubing for repair, inspection, or replacement. Occasionally, during production of the well, the tubing string becomes plugged in one or more places with sand, paraffin, or other contaminants requiring the removal of the tubing string to locate and remove the plugs.
The tubing string is raised a joint at a time. As each joint is raised from the well, it is unscrewed and checked for plugs. After the topmost joint of pipe has been removed from the next succeeding joint, the raising mechanism connects to the open end of the new top joint of pipe to continue the sequence of raising the tubing string. For those wells in which the fluids or gases are subjected to high pressures within the earth's formations, considerable danger exists during the extraction of the string because of the presence of high pressure product trapped or plugged in the tubing string. This pressure may suddenly be released upon disconnection of the sections of the tubing string.
In an effort to eliminate the hazards to life and property that this released pressure presents, pressure-control devices have been employed to contain this released pressure and allow for its controlled disposal.
A typical example of a prior-art pressure-control device for removing a plugged drill string is shown in U.S. Pat. No. 2,994,379 to C. C. Brown, et al. The prior-art pressure-control device exemplified by the above-mentioned patent includes a tubular body containing a pair of sealing units located at opposite ends of the body. The sealing units have a central opening through which the tubing string passes. The body contains two side connections. A pressure gauge in series with a release valve is secured to one of the side connections while a disposal line in series with a second release valve is secured to the opposite connection. The release valve and disposal line are used to bleed off the pressurized fluid from the interior of the tubular body. The two sealing units are longitudinally spaced from each other to accommodate between them the threaded pipe connection of the tubing string that is next to be uncoupled. Located above and below the two sealing units are slip sets for gripping the tubing string above and below the threaded pipe connection.
In operation, the threaded pipe connection is disconnected with the connection located between the upper and lower sealing units. Having disposed of any released pressure, the upper joint is removed from the device. After removing the upper joint, a safety valve must be lowered through the uppermost slips, through the upper sealing unit and mated to the open end of the tubing string. This operation is complicated because of the weight involved and the fact that the crew cannot see the threads to be mated. The crew must use trial and error to engage the threads. While attempting to engage these threads, the crew must have their hands and bodies in contact with a safety valve and above the top of the pressure control device. Any jarring or bumping of the tubing string could cause the plug in the tubing to release and expose the crew to the blast of suddenly released pressure. It would also leave them with no immediate method of stopping the flow. Additionally, the sealing units of this prior-art pressure-control device were constructed with restricted internal diameter rubber sealing portions constantly in contact with the tubing being hoisted from the well. As a result, many tools and devices which were a part of the tubing string but of a greater outside diameter than the tubing, could not be hoisted through the pressure-control device.
It is an improvement, therefore, to provide a pressure-control device in which the open end of the tubing string following disconnection of the topmost joint of pipe can be exposed above the pressure control device for connection to the safety valve without exposing the crew to unnecessary dangers. It is a further improvement to provide a pressure containing device that can be elevationally adjusted relative to the threaded pipe connection to position the sealing units relative to the threaded pipe connection. It is also an improvement to provide a pressure-containing device with a blowout preventor that can be positioned above the open end of the tubing string, and closed to shut off any uncontrolled flow of pressurized fluids or gases from the open end of the tubing string. It is also an improvement to provide a pressure-control device having an internal bore diameter larger than the largest outside diameter of the drill string so that the drill string may be raised unobstructed through the pressure-control device. It is also an improvement to provide a pressure-control device that can be coaxially aligned with the axis of the tubing string, to permit lifting of the string without interference with the internal bore of the device. It is also an improvement to provide a pressure-control device capable of permitting upward movement of the pressure-containing device as the threaded pipe connection is unscrewed and to absorb the shock of any released pressure tending to force the unscrewed top length of tubing out of the pressure-containing device.